1. Field of the Invention
The invention relates to a lighting apparatus. Particularly, the invention relates to a lighting apparatus for a fluorescent tube with an open-loop protection function and an over-voltage protection function, and a driving method thereof.
2. Description of Related Art
A fluorescent tube is widely used in today's lighting apparatus such as application domains of indoor lighting and backlight modules of display panels, etc. due to its advantages of low working temperature, high light-emitting efficiency, long service life and multiple colors, etc. An electric power conversion circuit is also referred to as an inverter, which is generally used to drive/light a cold cathode fluorescence lamp (CCFL). The inverter receives a direct current (DC) input voltage, and provides an alternating current (AC) driving voltage to the CCFL.
There are two methods for lighting the fluorescent tube: a single high-voltage method and a dual high-voltage method. The single high-voltage method refers to that one end of the fluorescent tube receives a driving voltage provided by the inverter, and the other end of the fluorescent tube is electrically connected to the ground, so that the fluorescent tube is lighted. In an example, the single high-voltage method is also referred to as a lighting method with a high voltage of one side and a low voltage of the other side.
However, based on the single high-voltage method, the lighting apparatus is operated in a positive voltage cycle during a certain period and operated in a negative voltage cycle during another period, which may lead to a low energy conversion efficiency and cause temperature increase of power components in the lighting apparatus, so that a service life of the fluorescent tube is decreased. Comparatively, the lighting apparatus using the dual high-voltage method is to use an electronic device to elevate voltage levels at two ends of the fluorescent tube, so that an AC driving voltage generated by the inverter is only required to oscillate at a single voltage level, for example, the AC driving voltage can be elevated to the positive voltage level. Compared to the single high-voltage method, the dual high-voltage method has a better energy conversion efficiency, which avails reducing a temperature increasing speed of the power device.
The fluorescent tubes in the market are generally lighted through the single high-voltage method, and such type of the lighting technique generally implements circuit protection measures such as open-loop protection and over-voltage protection according to a voltage signal in the fluorescent tube that is close to a ground voltage since the low voltage signal is easy to process, and the circuit protection measures have to be implemented in actual applications. On the other hand, since the driving technique of the dual high-voltage method is novel, and the two ends of the fluorescent tube are all applied with high voltage signals, the conventional circuit protection measure is hard to convert the high voltage signals. In this way, in order to innovate and break through the present known driving technique for the fluorescent tube, the circuit protection measure suitable for the dual high-voltage method is an important issue to be developed in the domain.